Past being strained? (5)
I believe the answer is:
tense
I believe this clue is a double definition.
'past' is the first definition.
(past tense)
'being strained?' is the second definition.
('tense' can be similar in meaning to 'strained')
(Other definitions for tense that I've seen before include "It may be perfect" , "Rigid; verb form" , "past possibly" , "Anxious - future, perhaps?" , "fraught" .)